Reversible motor control having alternatively operative dual amplifiers and automatic response adjustment

ABSTRACT

A drive system including a d-c motor has improved control means for generating a regulated control signal for controlling the supply of electric power to the motor. The control system includes a first amplifier operative when a net positive input signal is supplied thereto, a second amplifier operative when a net negative input signal is supplied thereto, means for supplying a command signal having a polarity and magnitude representative of desired motor performance to each amplifier, means for supplying a negative polarity signal representative of actual motor performance to the first amplifier and a positive polarity signal representative of actual motor performance to the second amplifier, and means for producing in response to the output of said amplifiers the regulated control signal. The control system also includes stabilizing means common to the two amplifiers and means for automatically adjusting the response of the amplifiers.

United States Patent Born et al.

[451 May 23,1972

[54] REVERSIBLE MOTOR CONTROL HAVING ALTERNATIVELY OPERATIVE DUALAMPLIFIERS AND AUTOMATIC RESPONSE ADJUSTMENT [72] Inventors: Norman E.Born; Edwin E. Kolatorowicz;

' Harry A. Plumb, Jr., all of Erie, Pa.

[73] Assignee: General Electric Company [22] Filed: May 5, 1970 [21Appl. No.: 34,709

[56] References Cited UNITED STATES PATENTS 3,419,777 l2/l968 Asseo..3l8/33l X Primary Examiner-J. D. Miller Assistant Examiner-Robert J.Hickey Attorney-James C. Davis, Jr., Edward W. Goebel, Jr., Frank L.Neuhauser, Oscar B. Waddell and Joseph B. F orman ABSTRACT A drivesystem including a d-c motor has improved control means for generating aregulated control signal for controlling the supply of electric power tothe motor. The control system includes a first amplifier operative whena net positive input signal is supplied thereto, a second amplifieroperative when a net negative input signal is supplied thereto, meansfor supplying a command signal having a polarity and magnituderepresentative of desired motor performance to each amplifier, means forsupplying a negative polarity signal representative of actual motorperformance to the first amplifier and a positive polarity signalrepresentative of actual motor performance to the second amplifier, andmeans for producing in response to the output of said amplifiers theregulated control signal. The control system also includes stabilizingmeans common to the two amplifiers and means for automatically 3,388,3076/1968 Prapis et al. .....3l8/434 adjusting the response fth lifi3,457,485 7/1969 Leonard ..3l8/257 8 Claims, 3 Drawing Figures I l I Ir50 i I I I Patented May 23, 1972 2 Sheets-Sheet 2 REVERSIBLE MOTORCONTROL HAVING ALTERNATIVELY OPERATIVE DUAL AMPLIFIERS AND AUTOMATICRESPONSE ADJUSTMENT I BACKGROUND OF THE INVENTION This invention relatesto motor control systems, and more specifically to closed-loop,regulated motor control systems. The invention is particularlyadvantageous to systems which provide reversing, d-c motor operationover a wide speed range including both armature voltage and fieldweakening speed ranges.

In a reversing, d-c motor control system, for example, if the regulatedparameter of motor performance is speed, a speed sensor is employed. Thespeed sensor is often a tachometer generator either a-c or d-c driven ata speed proportional to the motor speed. The tachometer-generator,during its operation, provides an output, termed a feedback, which isessentially linearly proportional to its operating speed. In aclosed-loop system in which motor speed is regulated, a feedback signalis introduced into a summing junction for comparison with a commandreference signal. Any difference in the magnitudes of these two signalsis termed an error signal. It is the error signal which is amplified ina motor controller to a level at which it governs the motor performancewith respect to speed.

The foregoing treats of a conventional d-c motor speed regulating systemwith negative feedback. The term negative feedback indicates a feedbacksignal which is opposite in polarity to the command reference signal.Thus, the negative feedback signal tends to cancel the command referencesignal and, in fact, does so when the motor operates at precisely thelevel of performance which corresponds to the command reference signal.A feedback signal which is of the same polarity as the command referencesignal, so that it adds to this signal, is a positive feedback. Ifpositive feedback occurs inadvertently in a motor speed regulatingsystem, a runaway condition exists, since the error signal becomes thesum of the command reference and feedback signals rather than thedifference between them. The feedback signal, in this instance,increases with the speed of the drive motor, creating an everincreasingapparent error signal as motor acceleration continues, and may result insevere overspeed of the motor.

This positive feedback signal is most likely to occur during theinstallation of a motor control system employing both d-c commandreference and dc feedback signals since electrical connections betweenthe tachometer generator and the motor controller may be established bypersonnel unaware of the consequences of such an error.

-To provide a polarized d-c feedback signal, many motor control systemsinclude a full-wave rectifier bridge connected between the tachometergenerator and the motor controller. The feedback signal from thetachometer generator, whether a-c or d-c, is connected to the terminalsof the rectifier bridge at which a-c to be rectified is normallyintroduced. The terminals of the rectifier bridge from which d-c isnormally derived, are customarily connected one to an amplifier, and oneto a system commonbus in the motor controller. The motor controller thusreceives a d-c feedback signal of a specific polarity from either an a-ctachometer generator or a d-c tachometer generator connected in eitherpolarity to the bridge.

Application of the full wave rectifier bridge, as described, to areversing motor control system using a tachometer generator results in afeedback signal of fixed polarity regardless of the direction oftachometer generator rotation. Normally in a system employing suchrectification, the use of signal reversing contacts for the commandreference signal and/or the feedback signal is required and thetachometer generator is not connected to a common conductor of thecontrol system. This fioating" condition of the feedback circuitincreases its susceptibility to extraneous, unwanted noise pulsesinductively or capacitively coupled to the circuit.

In relation to the foregoing facets of motor control system operation,the amplifier stage of the present invention provides severalimprovements not included in conventional equipment. One accomplishedobjective resides in the capability of the amplifier stage to establisha polarity-reversible error signal and respond thereto with apolarity-reversible output with no signal reversing contacts in eitherthe command reference signal circuit or the feedback signal circuit.

Another objective of this invention is the provision of circuitry toaccommodate at the feedback signal input tenninals an electrical outputof a floating feedback source of a-c or of d-c without regard topolarity, and to derive therefrom a pair of equal d-c feedback signals,oppositely polarized. This provi-' sion virtually eliminates thepossibility of obtaining the potentially damaging positive feedbackmentioned earlier.

Another attained object of this invention is the inclusion in itsfeedback circuitry of a path for attenuating the previously mentionednoise which may develop in the feedback source or its connections to themotor control system.

Another problem associated with motor control systems relates to thosesystems having motors which are to be operated over a wide speed range.

It is well known that a conventional shunt wound d-c motor may beoperated over a wide speed range consisting of two segments. The firstsegment is obtained by supplying rated current to the shunt field of themotor and varying the voltage applied to the armature of the motorbetween zero and the rated value. This segment of the total motor speedrange is commonly known as the armature voltage or constant torque speedrange and extends upwards from zero speed to a base speed. Base speed ofa motor is that speed which results when the shunt field is operated atrated current and the armature of a motor is operated at its ratedvoltage level, with the motor operating at full load and at its intendedtemperature. The second segment of the total speed range is achieved bymaintaining the motor armature voltage at its rated level and reducingthe level of the shunt field current below its rated level. This secondsegment of the speed range of the motor is known as the field weakeningor constant horsepower speed range.

It is also well known in the motor control an that a motor operating inits constant horsepower speed range, say at twice its base speed,develops only one-half of the torque per ampere of armature currentwhich it develops in the constant torque speed range. With respect totorque, the motor suffers an inherent loss of gain as its speed isprogressively increased above base speed. Since torque is the parameterof motor performance governing the motors ability to accelerate ordecelerate both its own armature and a connected load, the motorsresponse to a change of either load or command reference signal isslower in its constant horsepower speed range than in its constanttorque speed range. To assure motor control system stability in theconstant torque speed range of the motor, where the motor response is amaximum, the response of the motor controller must be set at such alevel that operation of the motor in its constant horsepower, reducedresponse speed range is at less than optimism system gain.

It is another object of this invention to provide a motor control systemoperating over a wide speed range which is capable of rapid response toinput signal level changes in the field weakening, constant horsepowerspeed range without causing unstable operation in the constant torquespeed range.

Briefly stated and in accordance with one aspect of this invention, areversing motor control system includes a polarityreversible commandreference signal source, a feedback signal source having an electricaloutput and a pair of polarity-sensitive amplifier networks with inputand output circuits. The feedback signal source output is rectified intofeedback signal of definitely established polarity regardless of theactual polarity or wave shape and frequency of the electrical output ofthe feedback source. A command reference signal of a first polarityprovided at the input circuit of the amplifier networks energizes anoutput circuit of one of the amplifier networks so as to normally causemotor rotation in a first direction. A command reference signal of theopposite polarity provided at the input circuit of the amplifiernetworks energizes an output circuit of the other amplifier networkwhich normally causes motor rotation in the opposite direction. Acomparison of the magnitude of the feedback signals with that of thecommand reference signal yields an error signal indicative of adeviation in actual motor performance from the desired performance. Thiserror signal is processed in the amplifier network activated for thedesired direction of motor rotation. The ac-' tivated amplifier networkproduces an output which tends to establish correspondence between theactual motor performance and the desired motor performance.

As described in the Background of the Invention a dc motor operated at alevel of shunt field current which is less than the rated shunt fieldcurrent undergoes a reduction of torque.-The torque reduction diminishesthe ability of the motor to respond to sudden changes in the commandreference signal or in the motor load. In accordance with another aspectof this invention, the response of the motor control system ismaintained at a satisfactory level in spite of the reduction in motortorque and response capability by increasing the response rate of thecontrol portion of the system. A feedback signal indicates when themotor torque is reduced to a selected level at which the response of themotor control system is unsatisfactory. Amplifiers incorporated in motorcontrol systems normally employ a stabilizing network in whichcapacitors are used. The capacitors retard the rate of change ofimpressed error signals to provide stability in the system, and decreasethe response rate of the control portion of a system.

To increase the response of the system, a switching circuit whichprovides a signal-attenuating path and an additional discharge path forthe stabilizing capacitor is added to an amplifier network. When thefeedback circuit indicates that the motor torque capability is at theselected, reduced level, the switching circuit is activated. Thisincreases the response rate of the control portion of the motor controlsystem, and thus increases the response of the whole motor controlsystem. I The specification concludes with claims particularly pointingout and distinctly claiming the subject matter of this invention. Theorganization and manner of making and using this invention together withfurther objects and advantages of this invention may be best understoodby reference to the following description taken in conjunction with theaccompanying figures.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a typical motor controlsystem in block diagram form incorporating the instant invention;

FIG. 2 is a graph depicting the more pertinent characteristics of a d-cmotor; and

FIG. 3 is a schematic diagram of the instant invention.

vAn identification number assigned to any part or portion of a figureidentifies that same part or portion in whatever figure that numberappears.

DETAILED DESCRIPTION OF THE FIGURES For reasons of clarity only, thefollowing descriptions are directed to a motor control system whichserves to regulate the speed of a d-c motor included in that system. Theinvention disclosed is equally applicable to systems regulating anotherof the motor performance parameters, and is, in fact, not limited tomotor control systems.

FIG. 1 is a block diagram representing a motor control system in whichmotor performance is regulated with respect to speed. The regulatedspeed range of the motor includes both armature voltage and fieldweakening speed ranges.

In FIG. 1, a motor is shown with connections 12 and 14 to conduct powerbetween a power control unit 16 and the motor armature 18. The powercontrol unit 16, in response to a controlled input signal, meters thepower delivered to the motor armature 18 in accordance with the demandsof the motor control system. lf the power control unit 16 is to converta-c power from its power supply to d-c power for utilization in themotor armature 18, any of several technologies might be used in thepower control unit 16 to accomplish the power conversion. For example, amotor-generator set would perfonn the function. If static conversionwithout rotating machinery in the power control unit 16 were desired,the controlled power conversion from a-c to d-c might be performed byeither tube-type or solid state devices, capable of rectification, withreactor or firing pulse control to govern the d-c output to the motorarmature 18.

The motor 10 also includes a field winding 20 with conductors 22 and 24connecting it to its adjustable voltage exciter 26. The adjustablevoltage exciter 26, like the power control unit 16, may take any one ofseveral forms. Since it furnishes the power requirements of the motor 10shunt wound field 20, the adjustable voltage exciter 26 should possessthe capability of providing d-c power at a plurality of d-c voltagelevels. Such means as a rheostat, for example, driven by a motor mightbe used if the power supply is d-c. If an a-c power supply is employed,controlled power conversion employing controllable rectifiers, forexample, may be used.

A speed sensor 28 is indicated as mechanically coupled to the motorarmature 18. The speed sensor may comprise a tachometer generator havingeither an a-c or d-c output or it may include a pulse generator togetherwith a digital-toanalog converter. In reality, the speed sensor 28 maybe coupled directly or indirectly to the motor armature 18, the onlyrequirement being that it be positively coupled to operate at a speedproportional to that of the motor armature 18. Two leads, 30 and 32,interconnect the speed sensor 28 with an amplifier stage 34 throughfeedback input terminals 36 and 38 included in the amplifier stage 34.In accordance with this invention, the speed sensor 28 may supply afeedback which is either an ac voltage or a d-c voltage to terminals 36and 38, and without regard to polarity, if it is a d-c voltage.Rectification means, hereinafter described, provide for theaccommodation and definite polarization in the amplifier stage 34 ofthis diversity of electrical feedbacks.

Also terminated in the amplifier stage 34, at terminal 40, is a commandreference signal. Three terminals 42, 44, and 46 provide for connectionsbetween a three wire control power supply 48 and the amplifier stage 34,and are respectively the positive, the negative and the common orneutral interconnections. Interposed between the command referencesignal terminal 40 of the amplifier stage 34 and the command signalsource 50 is a block 52 representing any of a variety of possiblecommand signal modifiers. A typical modifier in this location is a unitwhich provides a linearly changing output with respect to time, inresponse to a step-type input from the command signal source 50. Thecommand signal source 50, indicated as a potentiometer-connected devicein FIG. 1, may take any of several fonns. A primary requirement is thatin any form, it shall be capable of delivering an output of one voltagepolarity with respect to a common system bus per direction of motorrotation desired. As shown, the command signal source 50 may be adjustedto yield either a positive output voltage or a negative output voltagewith ready means for a transition from one polarity to the other.Similar facility for the provision of the required output prevails inmany computers and process controllers. If the motor control system ofFIG. 1 were to be operated as a slave drive to another such system, thecontrol power supply 48 and the command signal source 50 might both bereplaced, for example, by the output of a tachometer generator.

In accordance with this invention the reference signal applied toterminal 40 of the amplifier stage 34 may be of either positive ornegative polarity with respect to the system common at terminal 46,depending on the desired direction of rotation of the motor. Thereversible polarity of the reference signal allows the direction ofrotation of the motor 10 to be changed without using switch contacts.

From an output terminal 54 of the amplifier stage 34, an input signal issupplied to the power Control Unit 16 at a terminal 56 to govern itsperformance and its output to the motor armature 18. This input signalto the power Control unit 16 is of a magnitude proportional to anyvoltage difference existing within the amplifier stage 34 between thecommand reference signal, introduced at its terminal 40, and theelectrical feedback, introduced at its terminals 36 and 38. As it isshown in FIG. 1, the command signal source 50 has the capability offurnishing a polarity reversing signal to the command signal modifierrepresented by the block 52 if such a modifier is required in the motorcontrol system. The polarity reversing signal is not required if onlyunidirectional motor rotation is desired.

A control output terminal 58 of the power control unit 16 is connectedto the variable output voltage exciter 26 to control the level ofexcitation of the motor field 20. A control output terminal 60 of thevariable output voltage exciter 26 furnishes an input in the form of afeedback to the amplifier stage 34 at its terminal 62. It is the signalintroduced into the amplifier stage 34 at the terminal 62 which causes achange in the response of the amplifier stage 34. This response changecompensates for the inherent change of the motor 10 when it is operatedin its constant horsepower speed range at a reduced level of motor field20 excitation. An electrical connection 64 from the control outputterminal 58 of the power control unit 16 to the adjustable outputvoltage exciter 26 conveys an electrical signal which governs theinitiation and degree of motor field 20 excitation reduction.

A discussion of FIG. 2, immediately following, precedes an explanationof the operation of the motor control system of FIG. 1 to providefurther clarification.

FIG. 2 shows graphically a typical speed-torque characteristic of ashunt wound d-c motor such as is identified by the numeral 10 in FIG. 1.The curve is plotted against per unit values of speed and torque withper unit speed as the ordinate and per unit torque as the abscissa. Themotor operating condition termed base speed, previously defined in theBackground of the Invention, occurs at point A of FIG. 2. At point A themotor is operating at its rated torque, and its speed has been broughtto the rated base speed value by the application of rated armaturevoltage. Between zero speed and base speed, motor field excitation isheld constant at its rated value to enable the motor to develop itsrated torque. As mentioned earlier, the speed range indicated by thecurve seg ment A C" is variously known as the constant torque speedrange or the armature voltage speed range.

Motor speeds greater than base speed are obtainable by either furtherincreasing the voltage impressed on the motor armature to a value abovethe rated voltage or by reducing the motor field excitation. Sincefurther increase of armature voltage to a value in excess of its ratedvoltage cannot be recommended, field weakening with progressivelydiminishing torque is employed. The curve segment A B in FIG. 2 portraysthe diminution of output torque which occurs in a typical 4:l motorspeed range provided by motor field weakening. A ratio expression suchas the 4:1 employed above and shown in FIG. 2 is often used to definethe relationship of top motor operating speed to the base speed of themotor. To fulfill the term Constant Horsepower Speed Range, sincehorsepower is the product of torque and speed, as speed increases thetorque must decrease. FIG. 2 shows this relationship clearly where atpoint B, for example, the motor speed is four times its base speed andthe torque is reduced to one fourth of its base speed value. Thisreduction in the torque output of the motor at speeds in excess of motorbase speed reduces the ability of the motor to respond to a change inthe command reference signal. The change in this command referencesignal may correspond to either acceleration or deceleration of themotor and its load.At a reduced torque capability, the motor requires alonger period of time to accomplish a speed change corresponding to thechange in the command reference signal, as compare to an identicalchange at or below motor base speed. This reduction in response rate inthe field weakening speed range is the inherent response capabilitychange of a d-c shunt wound motor mentioned earlier.

The operation of the motor control system of FIG. I is so closelyrelated to the graph of FIG. 2 that the ensuing description of operationof FIG. 1 refers frequently to FIG. 2.

Assume that the motor 10 of FIG. 1 is to be accelerated from rest to apercent speed corresponding to point "B" of FIG. 2 and has a 4:l speedrange. Assume also that those power supplies required are connected,that the command reference signal at terminal 40 of the amplifier stage34 of FIG. 1 is zero, that a positive command reference signalcorresponds to forward motor rotation and that a command referencesignal of 100 percent corresponds to the top operating speed representedby point B" of FIG. 2.

As the command reference signal at its input tenninal 40 to theamplifier stage 34 of FIG. 1 is increased from zero to +25 percent, themotor I0, FIG. 1, accelerates to one-fourth of its top operating speed.The amplifier stage 34, through its output terminal 54 supplies an inputsignal to the power control unit 16 at its input terminal 56. Inresponse to this input signal, the power control unit 16 output voltageto the motor armature 18 increases from zero to the rated value. Thevariable output voltage exciter 26 maintains rated current in the motorfield 20, and the motor, having a 4:1 speed range, has traversed itsconstant torque speed range -the C A segment of FIG. 2. The speed sensor28 of FIG. 1 accelerates with the motor 10, and delivers a feedbackproportional to its speed to the amplifier stage 34. When this feedbackis properly proportional to the command reference signal, a comparisonpoint within the amplifier stage 34 arrests the output voltage increaseof the power control unit 16 and maintains it at essentially theattained level. The motor 10 acceleration is thereby terminated and itsspeed is held substantially constant at a value corresponding to point Aof FIG. 2.

It is to be noted that, though the speed-torque curve of FIG. 2 C A B"is not linear, a graph of the motor speed plotted against the commandreference signal yields a straight, unbroken line. This is true sincethe motor control system of FIG. 1 is linear with respect to motor 10speed the assumed regulated performance parameter.

To continue the motor 10 FIG. 1 acceleration to its 100 percent speedcorresponding to point B of FIG. 2, the command reference signal appliedto input terminal 40 FIG. I of the amplifier stage 34 is adjusted fromits +25 percent setting to its +100 percent value. This, in a pure speedregulator as shown, increases the signal level at the output terminal 54of the amplifier stage 34 to the input terminal 56 of the power controlunit 16 proportionately.

Unlike the earlier discussed change of the command reference signal fromzero to +25 percent which raises the power control unit 16 outputvoltage to the motor armature 18 from zero volts to rated voltage,changes in the command reference signal beyond the +25 percent level donot significantly alter the voltage applied to the motor armature 18.This voltage is held at its attained value of armature 18 rated voltageand the variable voltage exciter 26 output to the motor 10 shunt field20 is reduced. The reduction of shunt field 20 current initiates motor10 acceleration in its constant horsepower speed range with a diminutionof output torque as portrayed in FIG. 2 by the curve segment A" B.

The variable voltage exciter 26 output to the motor field 20 is governedby a signal indicative of motor 10 operation at the rated voltage of themotor 10 armature l8, and is derived from the power control unit 16 andintroduced through the electrical connection 64 to an input terminal 66of the exciter 26. This signal causes progressively diminishingadjustable voltage exciter 26 output as the command reference signalprogresses from +25 percent to +100 percent of its value.

The adjustable voltage exciter 26 also provides a control output at itstenninal 60. This control output connects to the amplifier stage 34 atterminal 62, and, in accordance with this invention, adjusts theamplifier stage 34 response. As

discussed previously, the adjustment of response of the amplifier stage34 is made to improve the response and accuracy of the total motorcontrol system of FIG. 1. This change compensates for the motor 10change illustrated in FIG. 2 by the curve A" B" as speeds in theconstant horsepower speed range are employed. In response to the earliermentioned +100 percent command reference signal, the motor 10 increasesin speed to its top operating level.

If the power control unit 16 of FIG. 1 is of a fully reversing type,properly protected, the motor 10, now operating at 100 percent speed inthe forward direction may be decelerated to zero speed andre-accelerated in a reverse direction. To accomplish this without theuse of contacts in the motor control system of FIG. 1 requires only thatthe command reference signal at input terminal 40 of the amplifier stage34 be shifted from its 100 percent forward value to a value of reversedpolarity corresponding to the desired reverse speed. Acceleration in thereverse direction involves the same operation as outlined above for theforward direction, but with a reversed polarity command reference signalassumed. If the reversing power control unit 16 is of the type whichpermits regenerative operation, whereby the kinetic energy of the motor10 and its load maybe returned to the power source on deceleration, asmooth, stepless reversal is experienced. Other means of driveretardation than regeneration may be employed but may result in a lesssmooth transition from rotation in one direction to rotation in theopposite direction.

FIG. 3 shows in detail the components and the circuitry included in theamplifier stage 34 of FIG. 1. Terminals for interconnecting theamplifier stage with other items shown in FIG. 1 are similarly numberedin FIGS. 1 and 3. For ease of discus sion and clarity of definition,functional groups within FIG. 3 are set apart by the use of brokenlines.

An output bridge 70 connected to first and second amplifiers, 72 and 74,respectively, furnishes a signal through out ut terminal 54 to the powercontrol unit 16 of FIG. 1. A stabilizing circuit 76, FIG. 3, couples anoutput circuit 78 of the firstamplifier 72 and an output circuit 80 ofthe second amplifier 74 to signal input circuits 82 and 84 of the firstand second amplifiers 72 and 74, respectively. A substantially inherentrelationship between stability and response prevails in a motor controlsystem, and is dealt with in detail in the subsequent discussion of thesystem operation.

The stabilizing circuit 76 has an output bridge including resistors 86and 88. A feedback bridge of the stabilizing circuit 76 includingresistors 90 and 92, connects the signal input circuit 82 of the firstamplifier 72 to the signal input circuit 84 of the second amplifier 74.A junction 94 between the resistors 90 and 92 of the stabilizing circuit76 is electrically connected through a resistor 96 in series with acapacitor 98 to an adjustable slider 100 of a firstpotentiometer-connected resistance unit 102. The firstpotentiometer-connected resistance unit 102 provides an electricalcircuit from a junction 104 between the resistors 86 and 88 of theoutput bridge to a common bus 108 through a junction 106. It is by meansof adjusting the slider 100 that the stabilizing circuit 76 provides forsetting the initial levels of response and stability of the amplifierstage 34 FIG. 1.

In addition to the signal input circuits 82 and 84, positive andnegative power supply busses 110 and 112, respectively, and thecommonbus 108 are connected to the amplifiers 72 and 74. Oppositely polarizeddiode rectifiers 114 and l 16 are connected between the signal inputcircuits 82 and 84 and the output circuits 78 and 80 of the first andsecond amplifiers 72 and 74, respectively. The function of these dioderectifiers 114 and. 116 is included hereinafter in the description ofoperation of the amplifier stage 34. Details of the first and secondamplifiers 72 and 74 are not shown in the figures, being well known inthe operational amplifier art.

In accordance with one aspect of this invention, an automatic responseadjust circuit 118 includes an input resistor 120, a semiconductordevice such as a thyristor or transistor 122 and a shunting resistor124. The input resistor 120 is interposed between the input terminal 62and the control electrode 126 of the device 122. The emitter 128 of thetransistor 122 is connected to the common bus 108 and the transistor 122collector is connected to one end of the shunting resistor 124. Theopposite end .of the shunting resistor 124 connects to the junction 94between resistors and 92 in the feedback bridge of the stabilizingcircuit 76.

Another functional block of the amplifier stage 34 of FIG. 3 is acommand signal input circuit 130 including resistors 132 and 134 in abridge circuit. The aforementioned command reference signal, introducedat the terminal 40 of the amplifier stage 34, is connected to a junction136 between the resistors 132 and 134 at the center of the bridgecircuit. Connections from the resistors 132 and 134 to the signal inputcircuits 82 and 84 of the first and second amplifiers 72 and 74,respectively, complete the command signal input circuit 130.

In accordance with another aspect of this invention are two functionalblocks, both related to processing the aforementioned electricalfeedback derived from the speed sensor 28 of FIG. 1. This feedback isdelivered to the amplifier stage 34 through the feedback input terminals36 and 38 for processing in a feedback signal input bridge circuit 138and a feedback adapter 140.

The feedback signal input bridge circuit 138 includes six resistors 142,144, 146, 148, 150, and 152, and a second potentiometer-connectedresistance unit 154 with an adjustable slider 156. The adjustable slider156 provides a ready means of establishing the relationship of thefeedback signal input bridge circuit to the common 108 through itsconnection thereto. The common bus 108 serves as a zero referencethroughout the entire motor control system of FIG. 1. The resistors 142,144, 146 and 148 together with the second potentiometer-connectedresistance unit 154, in a series circuit relationship, form abridge-type circuit which interconnects the signal input circuits 82 and84 of the first and second amplifiers 72 and 74, respectively. Resistors150 and 152 introduce the feedback signal into the bridge-type circuitat junctions 155 and 157, respectively. The feedback signal isintroduced into resistors 150 and 152 by means of their respectiveconnections 158 and 160 to the feedback adapter 140.

The feedback adapter includes energy-storing, filter capacitance 162 anda full wave single phase rectifier bridge 164. A midpoint 166 of thecapacitance 162 is connected to the common bus 108. Extremities of the,capacitance 162 and the polarized output of the full wave rectifierbridge 164. are electrically connected to the connections 158 and 160for introduction into the feedback signal input bridge circuit 138. Thefull wave rectifier bridge 164 includes four rectifier junctions, 167,168, 170 and 172. The rectifier bridge 164 has a positive output 174 anda negative output 176 coupled respectively through the connections 158and 160 to the input bridge circuit 138. Input connections to therectifier bridge 164 are 178 and 180 connected to feedback inputterminals 36 and 38, respectively, of FIGS. 1 and 3. It is to theseinput terminals 36 and 38 that the electrical feedback proportional tomotor speed, derived from the speed sensor 28 FIG. 1, is introduced.

The command reference signal, introduced at the terminal 40, determinesthe motor 10 direction of rotation and the motor 10 speed by itspolarity and magnitude, respectively. The feedback from the speed sensor28 may be either a-c voltage or randomly polarized d-c voltage. Theensuing description of the operational details of the amplifier stage 34further clarifies its versatility and applicability to closed-loopregulating systems.

The earlier discussion of the operation of the motor control system ofFIG. 1 touched briefly on the function of the amplifier stage 34indicated therein as one of the system blocks. The other blockscomprising the system are well known in the motor control system art andare, therefore, not detailed. The amplifier stage 34 of FIG. 1 isdetailed in FIG. 3 in a preferred embodiment to clarify this inventionand permit its complete analysis. Consistent with the earlierdescription, the following discussion of operation presupposes a motorcontrol system in which the motor 10, FIG. 1, is speed-regulated.

Considering in detail the operation of the amplifier stage 34, it willbenotcd with reference to FIG. 1 that its basic interconnections involvea quantity of eight identified terminals. These terminals, identicallyidentified in FIG. 3, comprise the various input points, the primaryoutput terminal and the common bus connection.

The command reference signal terminal 40 serves to introduce into theamplifier stage 34 through the command signal input circuit 130 a d-csignal proportional to the desired speed of the motor of FIG. 1. The d-csignal may be of either positive or negative polarity and, as previouslymentioned, may alternate between polarities if the motor control systemapplication required reversible motor 10 operation. Coincidentally withmotor 10 response to the command reference signal, the speed sensor 28supplies a feedback through the feedback input terminals 36 and 38. Thefeedback is proportional to the motor 10 attained speed and isintroduced into the feedback adapter 140, FIG. 3, of the amplifier stage34. By virtue of the full wave rectifier bridge 164 input connections158 and 160 to the normal a-c inputs, the feedback adapter 140 acceptseither an a-c feedback, or a d-c feedback. The d-c feedback may beapplied with either feedback input terminal 36 or 38 positive withrespect to the other. Rectification in the full wave rectifier bridge164 produces a d-c feedback signal which is definitely and unalterablypolarized. The feedback signal in invariably positive at the rectifierbridge 164 output terminal 174 and negative at the output terminal 176.These polarities prevail with respect to each other and with respect tothe systems common bus 108. The dual filter capacitance 162 permitsattenuation of ripple or noise present in the feedback signal. A pathfor the ripple to the common bus 108 is provided by the midpoint 166connection of the dual capacitance 162 to the common bus 108. Thefiltered, definitely polarized d-c feedback signal is delivered to thefeedback signal input bridge circuit 138 through the connections 158 and160.

The feedback signal input bridge circuit 138, like the other bridgecircuits to be discussed later, includes a balanced resistance bridge.The resistors 150 and 152 are of the same nominal ohmic value.Similarly, it is intended that the resistors 142 and 144 equal theresistance value of the resistors 146 and 148, respectively. To insurethe capability of balancing the feedback signal input bridge circuit138, the second potentiometer-connected resistance unit 154 is employedat the theoretical center of the bridge circuit 138. By means of theadjustable slider 156 on the potentiometer-connected resistance unit 154a precise balance is obtainable with reference to the common bus 108 towhich the adjustable slider 156 is connected as shown. It will beappreciated that a lack of balance in this feedback signal input bridgecircuit 138 is reflected in an inequality of the feedback signalinfluence on the signal input circuits 82 and 84 of the first and secondamplifiers 72 and 74, respectively. Functionally, in the event of animbalance, the motor 10, FIG. 1 would be driven faster in one directionthan in the other by command reference signals of equal magnitude but ofopposite polarities.

The positive and negative d-c output of the feedback signal input bridgecircuit 138, FIG. 3 connect directly to the signal input circuits 82 and84, respectively, of the first and second amplifiers 72 and 74,respectively, In the signal input circuits 82 and 84, these positive andnegative feedback signals are compared to the output of the commandsignal input circuit 130.

The command signal input circuit 130 also includes a balanced bridge inwhich the resistors 132 and 134 are nominally of equal value. Thecommand reference signal, introduced at input terminal 40, is connectedto the junction 136 at the center of the balanced bridge between theresistors 132 and 134. The outputs of the command signal input circuit130 from the extremities of the resistors 132 and 134 are connected tothe signal input circuits 82 and 84, respectively, of the first andsecond amplifiers 72 and 74, respectively. A resultant combination withthe polarized feedback signal on the signal input circuits 82 and 84provides the aforementioned signal comparison and results in anoperating error signal.

By its magnitude, the operating error signal indicates the extent of anyexisting discrepancy between the motor 10, FIG. 1 attained speed and thedesired motor 10 speed. The desired motor 10 speed is that whichcorresponds to the value of the command reference signal introduced intothe command signal input circuit 130, FIG. 3 at the terminal 40.

Further discussion of the operation of the reversible amplifier stage 34is facilitated by the assumption of a definite polarity for thepolarity-reversible command reference signal introduced at the terminal40 of the amplifier stage 34. A command reference signal of eitherpositive or negative d-c polarity operates the amplifier stage 34 in anidentical manner, but activates alternate components. As previouslymentioned, the processed feedback signal impresses a positive d-c valueon the signal input circuit 82 of the first amplifier 72, and a negativevalue on the signal input circuit 84 of the second amplifier 74. Forpurposes of discussion and clarification, a positive d-c commandreference signal of finite magnitude is assumed. Also assumed isacceleration of the motor 10 FIG. 1 toward its speed level correspondingto the assumed command reference signal. The command signal inputcircuit 130, FIG. 3 into which the command reference signal isintroduced through the terminal 40 impresses this positive d-c commandreference signal equally on the signal input circuits 82 and 84 of thefirst and second amplifiers 72 and 74, respectively. This activates bothof the amplifiers 72 and 74 in which, as is customary, a polarityinversion occurs. A negatively polarized d-c output of the first andsecond amplifiers 72 and 74, respectively, is thus created in theirrespective output circuits 78 and 80. These outputs are combined in thefirst output bridge circuit 70 and a signal proportional to the sum ofthese outputs appears at the output terminal 54 of the amplifier stage34. As the motor 10, FIG. 1 responds to the effect of this output on thepower control unit 16, the speed sensor 28 output level increases. Thiscreates an increasingly positive feedback signal at the signal inputcircuit 82 FIG. 3 of the first amplifier 72, additive to the assumedpositive command reference signal. COnversely, at the signal inputcircuit 84 of the second amplifier 74, an increasingly negative feedbacksignal is experienced. Thus, as referred to the common bus 108, theerror signal at the first preamplifier 72 signal input circuit 82becomes increasingly positive as the motor 10 FIG. 1 accelerates. Theerror signal at the signal input circuit 84 of the second amplifier 74becomes progressively and correspondingly less positive with referenceto the common bus 108. The error signal at signal input circuit 84becomes an operating error signal when a command reference signal ofpositive d-c polarity is employed.

Resistors and 92 of the stabilizing circuit 76 serve as buffer resistorsand prevent undue transfer between the operating error signal applied tothe second amplifier 74 and a non-operating error signal extant at thesignal input circuit 82 of the first amplifier 72.

The diode rectifier 1 14 is so polarized as to prevent the nonoperatingerror signal, representative of the sum of the positive commandreference signal and the positive portion of the feedback signal, fromamplification in the first amplifier 72.

The diode rectifier 114 associated with the first amplifier 72 wouldconduct the positive non-operating error signal at the signal inputcircuit 82 to the output circuit 78 were not this non-operating signalinverted in the first amplifier 72. A negative voltage on the outputcircuit 78 in excess of the low forward blocking voltage of the dioderectifier 114 biases that diode rectifier into its conductive state. Inthis conductive state, the diode rectifier 114 becomes a local negativefeedback and serves as a gain limit or clamp with respect to the firstamplifier 72.

If the assumed polarity of the command reference signal were negativerather than positive, diode 116 would similarly limit or clamp the gainof the second amplifier 74. Under the presently assumed operatingconditions with the positive command reference signal, the diode l 16 isback biased and maintained in its non-conductive state. These conditionseliminate the gain limit function of the diode 116, and permit normaloperating error signal amplification in the second preamplifier 74. Theoutput circuit 80 of the second amplifier 74 delivers the negative d-camplified operating error signal to the first output bridge circuit 70output terminal 54 for interconnection to the power control unit 16 ofFIG. 1.

As previously suggested, introduction of a negative d-c commandreference signal at the terminal 40, FIG. 1 of the command signal inputcircuit 130 yields identical operation of the amplifier stage 34. Inthis instance, an operating error signal occurs on the signal inputcircuit 82 of the first amplifier 72. The second amplifier 74 is clampedor gain limited by its associated rectifier 116 which is biased into itsconductive state by the non-operating error signal and the secondamplifier 74 output.

In accordance with another aspect of this invention, the amplifier stage34 includes an additional function in the form of the automatic responseadjustment circuit 118. This unit is functionally described in previousportions of this specification. A detailed operational discussion ofthis aspect follows in the succeeding paragraphs.

The automatic response adjustment circuit 118 function is so closelyallied with that of the stabilizing circuit 76 that commentary on thelatter is necessarily included in the discussion of the former.

A conventional stabilizing circuit operates to diminish the responserate of an operating amplifier paralleled thereby. The stabilizingcircuit 76, FIG. 3, effectively parallels both the first and secondamplifiers, 72 and 74, respectively. Considering the first amplifier 72for example, the parallel stabilizing circuit is provided by theseries-connected components including the resistor 86, the firstresistance unit 102, the slider 100, the capacitance 98, and theresistors 96 and 90. This series circuit connects the output circuit 78of the first amplifier 72 to the signal input circuit 82 of the firstamplifier 72, and

- becomes a local transient feedback circuit. Since the relative d-cpolarities of the signal input circuit 82 and of the output circuit 78are opposing, negative feedback as earlier defined, prevails. Theadjustability of the slider 100 on the first resistance unit 102 enablesthe establishment of a level of local transient feedback. The level isincreased as the slider 100 is moved toward the junction 104. Thissetting also increases the total impedance between the signal inputcircuit 82 and the common bus 108 at the junction 106, and theresistance between the capacitance 98 and the junction 106. Together,these increase reduce transient gain in the first amplifier 72 and theresponse of the first amplifier 72 is thereby minimized to yield maximumstability. If all portions of the motor control systems of FIG. 1maintained uniform gain throughout their operating range, a single,optimum setting of the slider 100, FIG. 3 would be possible. As pointedout with reference to FIG. 2, the motor of FIG. 1 experiences anincreasing loss of torque capability as it accelerates through itsconstant horsepower speed range.

It is apparent from the foregoing discussion of the stabilizing circuit76 of FIG. 3, and consideration of the motor torque change that optimumperformance of the motor 10 FIG. 1 is not attainable over its entirespeed range at a single setting of the slider 100 FIG. 3. A setting ofthe slider 100 which provides optimum motor performance in the constanttorque, armature voltage speed range yields slower motor response in itsconstant horsepower, field weakening speed range. If the slider 100 isadjusted to yield optimum performance in the higher speed range, systeminstability is likely in the lower speed range. The automatic transientgain adjustment circuit 118 is directed to a solution of this problem.

For the moment, consider the transistor 122 collector to emitter 130 to128 junction as non-conductive. In this state, the transistor 122 andthe automatic transient gain adjustment circuit 118 have no effect onthe response or transient gain of the amplifier stage 34. Thestabilizing circuit 76 is then adjusted to provide optimum performanceof the motor 10, FIG. 1 during its acceleration through its constanttorque speed range.

If acceleration of the motor 10 is continued into its constanthorsepower, shunt field 20 weakening speed range wherein reduced torquecapability prevails, the adjustable voltage exciter 26 outputdiminishes. When the diminution reaches an adjustable, predeterminedlevel corresponding to a given reduction in the torque capability of themotor 10, the adjustable voltage exciter 26 provides a control output atits terminal 60. This control output is impressed on the amplifier stage34 at terminal 62. Referring to FIG. 3, it will be noted that theterminal 62 is connected through the resistor to the base electrode 126of the transistor 122. By means of this connection, the control outputof the adjustable voltage exciter 26, FIG. 1 governs the automaticresponse adjustment circuit 118. Since the emitter 128 of the NPN typetransistor 122 connects directly to the common bus 108, a voltage whichis positive with respect to the common bus 108 applied at the baseelectrode 126 causes the transistor to assume its conductive state. Adiode rectifier 129 is interposed between the common bus 108 and thetransistor 122 base electrode 126 connection. The diode rectifier 129serves to protect the transistor 122, should a negative voltage beapplied the base electrode 126.

Unlike the previously considered situation with the transistor 122 inits passive state with no influence on the response of the amplifierstage 34, conductivity of the transistor 122 produces a responseincrease in the amplifier stage 34. During conductivity of thetransistor 122, the resistor 124 is effectively connected at one end tothe common bus 108. The second end of the resistor 124 is connectedthrough the junction 94 and the resistor 96 to the capacitance 98. Thecircuit thus established from the capacitance 98 to the common bus 108shunts current flowing through the capacitance 98 to the common bus 108,thereby decreasing the transient negative feedback to input circuits 82and 84. This increases the amplifier stage 34 response rate or transientgain. Since the value of response is readily adjustable by varying theohmic value of the resistor 124, changes in motor torque capability overa wide latitude may be compensated for by this invention.

Inspection of FIG. 3 in detail with respect tothe deployment andoperation of the transistor 122 reveals that its collectoremitterjunction, -128, must be made conductive regardless of the relativepolarization across that junction. This is a requirement since thetransistor 122 must be able to operate on either the first or secondamplifier, 72 or 74, respectively. This contradiction of the normalconcept of transistor operation is made possible by an abnormally largecurrent in the base 126 circuit. Many transistors display such a loss ofpolarity discrimination in their collector-emitter junctions if circuitparameters are such that their base current exceeds their emittercurrent.

This invention is notlimited to the specific details of the preferredembodiment illustrated. It is contemplated that many changes to andmodifications of this embodiment will occur to those skilled in the art.As examples, with respect to the transient gain adjust feature, aplurality of gain change steps may be used or the automatic transientgain adjustment circuit 118 may be employed with an amplifier stageincluding a single amplifier. With respect to the feedback adapter 140,if the feedback thereto is always of identically polarized d-c, thefeedback adapter is superfluous. It is, therefore, intended that theappended claims cover all such changes, additions and modifications asfall within the true spirit and scope of this invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In a drive system including a d-c motor and power conversion meansfor supplying electric power to the armature and field of the d-c motorin response to a regulated control signal, improved control means forgenerating the regulated control signal comprising:

a. means for producing a d-c command signal having a magnitude andpolarity representative of desired motor performance,

b. means for producing an electric feedback signal having a magnituderepresentative of attained motor performance,

c. first amplifying means including input means and output means,

d. second amplifying means including input means and output means,

e. first network means including rectifying means coupled to saidfeedback signal producing means and said input means of each of saidfirst and second amplifying means and being responsive to the feedbacksignal to supply a positive polarity signal to said first amplifyingmeans and a negative polarity signal to said second amplifying means,said positive and negative polarity signals having magnitudesrepresentative of attained motor performance,

f. second network means coupled to command signal producing means andsaid input means of said first and second amplifying means andresponsive to the command signal to supply to each of said input means ad-c signal having a magnitude and polarity representative of desiredmotor performance,

g. said first amplifying means being operative when the signals suppliedthereto by said first and second network means have a net negativepolarity and said second amplifying means being operative when thesignals supplied thereto by said first and second network means have anet positive polarity,

h. and third network means coupled to said output means of each of saidfirst and second amplifying means for receiving output signals therefromand producing in response thereto a regulated control signal fordelivery to the power conversion means.

2. Control means according to claim 1 in which said means for providingan electric feedback signal having a magnitude representative ofattained motor performance comprises means coupled to the motor tooperate at a speed proportional to that of the motor armature.

3. Control means according to claim 1 further comprising stabilizingmeans interconnecting said first and second amplifying means tostabilize the operative ones of said amplifying means during generationof a regulated control signal.

4. Control means according to claim 1 in which each of said first andsecond amplifying means includes rectification means disposed such thatsaid first amplifying means is inoperative when the net signal suppliedthereto is positive and such that said second amplifying means isinoperative when the signal supplied thereto is negative.

5. In control means for a drive system including a d-c motor and powerconversion means for supplying electric power to the armature and fieldof the d-c motor in response to a regulated control signal generated bythe control means, improved amplification means comprising:

first amplifying means,

second amplifying means,

first input circuit means connected to a command source to introducetherefrom a signal having a magnitude and polarity representative of adesired motor performance and direction of rotation,

second input circuit means coupled to the motor to introduce therefroman electrical feedback signal indicative of the attained motorperformance in the desired direction of rotation,

rectifier means connected to said second input circuit means to providea pair of feedback signals of opposite polarity proportional to, andregardless of the polarity, wave shape and frequency of the electricalfeedback signal, the attained motor performance,

circuit means connected to said first input circuit means, saidrectifier means, and said first and second amplifying means to supplythe signal representative of the desired motor performance to both ofsaid amplifying means and a selected one only of said feedback signalsto each of said amplifying means,

means connected to said first and second amplifying means to activatethe one of said amplifying means to which signals of opposite polarityare supplied,

common stabilizing means coupled to both of said first and secondamplifying means to stabilize the operative one of said amplifying meansduring generation of a regulated control signal,

and automatic response rate adjustment means coupled to the motor andsaid common stabilizing means to adjust the response rate of theoperative one of said amplifying means in response to changes in theresponse rate of the motor.

6. In a closed-loop motor control system including a drive motor withmeans responsive to the performance of the motor to create a feedbackproportional to a parameter of the drive motors performance; a powercontrol unit connectable to a source of electrical energy and to thedrive motor to supply power to the motor in accordance with an inputsignal to the power control unit; a three wire, regulated d-c controlpower supply connected to the power control unit; a source of commandsignals to govern the drive motors performance, also connected to thethree wire, regulated d-c power supply; and the improvement whichincludes an amplifier stage comprising in combination:

a. two amplifiers, each of which is connected to the aforesaidthree-wire regulated d-c control power supply;

b. a signal input circuit and an output circuit connected electricallyto each of said amplifiers;

c. diode rectifiers in parallel circuit relationship with each of saidamplifiers, the first of said diode rectifiers polarized to pass apositive signal from said signal input circuit of the first of saidamplifiers to said output circuit of said first amplifier, and thesecond of said diode rectifiers polarized to pass a negative signal fromsaid signal input circuit of the second of said amplifiers to saidoutput circuit of said second amplifier;

d. first and second output bridge circuits connecting said outputcircuit of said first amplifier to said output circuit of said secondamplifier, each of said bridge circuits comprising an essentiallycenter-tapped resistance including connection means at the center tap,the first of said output bridge circuits provides an output connectionfor said amplifier stage, said output connection being connectable tosupply the aforesaid power control unit with its aforesaid input signal;

e. a stabilizing circuit for said amplifier stage, said stabilizingcircuit comprising the second of said output bridge circuits, whichincludes a potentiometer-connected resistance unit electrically andserially connected between said output connection of said second outputbridge circuit and a common connection point of the aforesaidthree-wire, regulated d-c control power supply, saidpotentiometer-connected resistance unit having a third connection pointadjustable between its aforesaid connections to the output connection ofsaid second output bridge circuit and to said common connection point, aresistor and a capacitor in a series circuit configuration, saidcapacitor electrically connected to said third connection point of saidpotentiometer-connected resistance unit, said resistor terminating in ajunction point at the end remote from said capacitor, and a first inputbridge circuit including an essentially center-tapped resistance unit,said resistance unit electrically connected between said signal inputcircuits of said first and second amplifiers and including connectionmeans at the center tap, said connection means providing the junctionpoint for said resistor of said resistor and capacitor series circuit;

f. a command signal input bridge circuit, comprising an essentiallycenter-tapped resistance bridge unit, connected between said signalinput circuits of said first and second amplifiers, and includingconnection means at its center tap into which the aforesaid commandsignal source delivers a command signal representative of the desiredperformance of the aforesaid drive motor means with respect to aregulated parameter of drive motor performance;

. a feedback signal input bridge circuit comprising six resistors and apotentiometer-connected resistance unit, four of said resistors and theresistance unit of said potentiometer-connected resistance unit seriallyconnected, said resistance unit in the center, location wise andresistance wise, said four serially connected resistors and saidresistance unit forming a bridge circuit connected between said signalinput circuits of said first and second amplifiers, the first of theremaining two of said six resistors, each having a termination at oneend connected electrically at its end opposite the termination to ajunction between the two of said six resistors connected to a first endof said resistance unit, the other and final of the remaining two ofsaid six resistors connected electrically, at the end opposite itstermination, to a junction between the two of said six resistorsconnected to a second end of said resistance unit, a third andadjustable connection of said potentiometer-connected resistance unitelectrically connected to the common connection point of the aforesaid,three-wire regulated d-c power supply; and, a feedback adaptercomprising single-phase full wave rectifier means, having two a-c andtwo d-c junctions with filter means connected between its d-c junctions,said full wave rectifier means incorporating connection means toaccommodate the aforesaid feedback at its a-c junctions,

said filter means including center-tapped capacitive means withterminals at each end and at the center thereof, connection means toconnect the center terminal to the common connection point of theaforesaid threewire regulated d-c power supply and the end terminals ofthe capacitive means to the aforesaid terminations of the aforesaidremaining two of said six resistors in said feedback signal input bridgecircuit.

7. A closed-loop, motor control system according to claim 6, includingan automatic response rate adjustment means to compensate for reducedmotor torque capability, comprising in combination: a semi-conductordevice with four operative connections, having a resistive signal inputconnection to a control electrode, a reference connection between afirst electrode of said semi-conductor device and the aforesaid commonsystem bus, a protective connection incorporating a rectifier betweenthe first electrode of said semi-conductor device and said signal inputconnection, and an output connection from a second electrode of saidsemi-conductor device through a resistance to the aforesaid junctionpoint of the aforesaid first input bridge circuit, said automaticresponse rate adjustment means being responsive to a signal impressed onsaid signal input connection to establish an electrical path through ajunction of said semi-conductor device between said first electrode andsaid second electrode to provide an electrically conductive path fromthe aforesaid junction point of the aforesaid first input bridge circuitto the aforesaid common system bus.

8. A closed-loop motor control system according to Claim 7 wherein saidsemi-conductor device is a transistor.

1. In a drive system including a d-c motor and power conversion meansfor supplying electric power to the armature and field of the d-c motorin response to a regulated control signal, improved control means forgenerating the regulated control signal comprising: a. means forproducing a d-c command signal having a magnitude and polarityrepresentative of desired motor performance, b. means for producing anelectric feedback signal having a magnitude representative of attainedmotor performance, c. first amplifying means including input means andoutput means, d. second amplifying means including input means andoutput means, e. first network means including rectifying means coupledto said feedback signal producing means and said input means of each ofsaid first and second amplifying means and being responsive to thefeedback signal to supply a positive polarity signal to said firstamplifying means and a negative polarity signal to said secondamplifying means, said positive and negative polarity signals havingmagnitudes representative of attained motor performance, f. secondnetwork means coupled to command signal producing means and said inputmeans of said first and second amplifying means and responsive to thecommand signal to supply to each of said input means a d-c signal havinga magnitude and polarity representative of desired motor performance, g.said first amplifying means being operative when the signals suppliedthereto by said first and second network means have a net negativepolarity and said second amplifying means being operative when thesignals supplied thereto by said first and second network means have anet positive polarity, h. and third network means coupled to said outputmeans of each of said first and second amplifying means for receivingoutput signals therefrom and producing in response thereto a regulatedcontrol signal for delivery to the power conversion means.
 2. Controlmeans according to claim 1 in which said means for providing an electricfeedback signal having a magnitude representative of attained motorperformance comprises means coupled to the motor to operate at a speedproportional to that of the motor armature.
 3. Control means accordingto claim 1 further comprising stabilizing means interconnecting saidfirst and second amplifying means to stabilize the operative ones ofsaid amplifying means during generation of a regulated control signal.4. Control means according to claim 1 in which each of said first andsecond amplifying means includes rectification means disposed such thatsaid first amplifying means is inoperative when the net signal suppliedthereto is positive and such that said second amplifying means isinoperative when the signal supplied thereto is negative.
 5. In controlmeans for a drive system including a d-c motor and power conversionmeans for supplying electric power to the armAture and field of the d-cmotor in response to a regulated control signal generated by the controlmeans, improved amplification means comprising: first amplifying means,second amplifying means, first input circuit means connected to acommand source to introduce therefrom a signal having a magnitude andpolarity representative of a desired motor performance and direction ofrotation, second input circuit means coupled to the motor to introducetherefrom an electrical feedback signal indicative of the attained motorperformance in the desired direction of rotation, rectifier meansconnected to said second input circuit means to provide a pair offeedback signals of opposite polarity proportional to, and regardless ofthe polarity, wave shape and frequency of the electrical feedbacksignal, the attained motor performance, circuit means connected to saidfirst input circuit means, said rectifier means, and said first andsecond amplifying means to supply the signal representative of thedesired motor performance to both of said amplifying means and aselected one only of said feedback signals to each of said amplifyingmeans, means connected to said first and second amplifying means toactivate the one of said amplifying means to which signals of oppositepolarity are supplied, common stabilizing means coupled to both of saidfirst and second amplifying means to stabilize the operative one of saidamplifying means during generation of a regulated control signal, andautomatic response rate adjustment means coupled to the motor and saidcommon stabilizing means to adjust the response rate of the operativeone of said amplifying means in response to changes in the response rateof the motor.
 6. In a closed-loop motor control system including a drivemotor with means responsive to the performance of the motor to create afeedback proportional to a parameter of the drive motor''s performance;a power control unit connectable to a source of electrical energy and tothe drive motor to supply power to the motor in accordance with an inputsignal to the power control unit; a three wire, regulated d-c controlpower supply connected to the power control unit; a source of commandsignals to govern the drive motor''s performance, also connected to thethree wire, regulated d-c power supply; and the improvement whichincludes an amplifier stage comprising in combination: a. twoamplifiers, each of which is connected to the aforesaid three-wireregulated d-c control power supply; b. a signal input circuit and anoutput circuit connected electrically to each of said amplifiers; c.diode rectifiers in parallel circuit relationship with each of saidamplifiers, the first of said diode rectifiers polarized to pass apositive signal from said signal input circuit of the first of saidamplifiers to said output circuit of said first amplifier, and thesecond of said diode rectifiers polarized to pass a negative signal fromsaid signal input circuit of the second of said amplifiers to saidoutput circuit of said second amplifier; d. first and second outputbridge circuits connecting said output circuit of said first amplifierto said output circuit of said second amplifier, each of said bridgecircuits comprising an essentially center-tapped resistance includingconnection means at the center tap, the first of said output bridgecircuits provides an output connection for said amplifier stage, saidoutput connection being connectable to supply the aforesaid powercontrol unit with its aforesaid input signal; e. a stabilizing circuitfor said amplifier stage, said stabilizing circuit comprising the secondof said output bridge circuits, which includes a potentiometer-connectedresistance unit electrically and serially connected between said outputconnection of said second output bridge circuit and a common connectionpoint of the aforesaid three-wire, regulated d-c control power supply,said potentiometer-connected resistanCe unit having a third connectionpoint adjustable between its aforesaid connections to the outputconnection of said second output bridge circuit and to said commonconnection point, a resistor and a capacitor in a series circuitconfiguration, said capacitor electrically connected to said thirdconnection point of said potentiometer-connected resistance unit, saidresistor terminating in a junction point at the end remote from saidcapacitor, and a first input bridge circuit including an essentiallycenter-tapped resistance unit, said resistance unit electricallyconnected between said signal input circuits of said first and secondamplifiers and including connection means at the center tap, saidconnection means providing the junction point for said resistor of saidresistor and capacitor series circuit; f. a command signal input bridgecircuit, comprising an essentially center-tapped resistance bridge unit,connected between said signal input circuits of said first and secondamplifiers, and including connection means at its center tap into whichthe aforesaid command signal source delivers a command signalrepresentative of the desired performance of the aforesaid drive motormeans with respect to a regulated parameter of drive motor performance;g. a feedback signal input bridge circuit comprising six resistors and apotentiometer-connected resistance unit, four of said resistors and theresistance unit of said potentiometer-connected resistance unit seriallyconnected, said resistance unit in the center, location wise andresistance wise, said four serially connected resistors and saidresistance unit forming a bridge circuit connected between said signalinput circuits of said first and second amplifiers, the first of theremaining two of said six resistors, each having a termination at oneend connected electrically at its end opposite the termination to ajunction between the two of said six resistors connected to a first endof said resistance unit, the other and final of the remaining two ofsaid six resistors connected electrically, at the end opposite itstermination, to a junction between the two of said six resistorsconnected to a second end of said resistance unit, a third andadjustable connection of said potentiometer-connected resistance unitelectrically connected to the common connection point of the aforesaid,three-wire regulated d-c power supply; and, h. a feedback adaptercomprising single-phase full wave rectifier means, having two a-c andtwo d-c junctions with filter means connected between its d-c junctions,said full wave rectifier means incorporating connection means toaccommodate the aforesaid feedback at its a-c junctions, said filtermeans including center-tapped capacitive means with terminals at eachend and at the center thereof, connection means to connect the centerterminal to the common connection point of the aforesaid three-wireregulated d-c power supply and the end terminals of the capacitive meansto the aforesaid terminations of the aforesaid remaining two of said sixresistors in said feedback signal input bridge circuit.
 7. Aclosed-loop, motor control system according to claim 6, including anautomatic response rate adjustment means to compensate for reduced motortorque capability, comprising in combination: a semi-conductor devicewith four operative connections, having a resistive signal inputconnection to a control electrode, a reference connection between afirst electrode of said semi-conductor device and the aforesaid commonsystem bus, a protective connection incorporating a rectifier betweenthe first electrode of said semi-conductor device and said signal inputconnection, and an output connection from a second electrode of saidsemi-conductor device through a resistance to the aforesaid junctionpoint of the aforesaid first input bridge circuit, said automaticresponse rate adjustment means being responsive to a signal impressed onsaid signal input connection to establish an electrical path through Ajunction of said semi-conductor device between said first electrode andsaid second electrode to provide an electrically conductive path fromthe aforesaid junction point of the aforesaid first input bridge circuitto the aforesaid common system bus.
 8. A closed-loop motor controlsystem according to Claim 7 wherein said semi-conductor device is atransistor.